Sampling
Learn how to configure the volume of error and transaction events sent to Sentry.
Adding Sentry to your app gives you a great deal of very valuable information about errors and performance you wouldn't otherwise get. And lots of information is good -- as long as it's the right information, at a reasonable volume.
To send a representative sample of your errors to Sentry, set the sampleRate
option in your SDK configuration to a number between 0
(0% of errors sent) and 1
(100% of errors sent). This is a static rate, which will apply equally to all errors. For example, to sample 25% of your errors:
Sentry.init({sampleRate: 0.25});
The error sample rate defaults to 1
, meaning all errors are sent to Sentry.
Changing the error sample rate requires re-deployment. In addition, setting an SDK sample rate limits visibility into the source of events. Setting a rate limit for your project (which only drops events when volume is high) may better suit your needs.
We recommend sampling your transactions for two reasons:
- Capturing a single trace involves minimal overhead, but capturing traces for every page load or every API request may add an undesirable load to your system.
- Enabling sampling allows you to better manage the number of events sent to Sentry, so you can tailor your volume to your organization's needs.
Choose a sampling rate with the goal of finding a balance between performance and volume concerns with data accuracy. You don't want to collect too much data, but you want to collect sufficient data from which to draw meaningful conclusions. If you’re not sure what rate to choose, start with a low value and gradually increase it as you learn more about your traffic patterns and volume.
The Sentry SDKs have two configuration options to control the volume of transactions sent to Sentry, allowing you to take a representative sample:
Uniform sample rate (
tracesSampleRate
):- Provides an even cross-section of transactions, no matter where in your app or under what circumstances they occur.
- Uses default inheritance and precedence behavior
Sampling function (
tracesSampler
) which:- Samples different transactions at different rates
- Filters out some transactions entirely
- Modifies default precedence and inheritance behavior
By default, none of these options are set, meaning no transactions will be sent to Sentry. You must set either one of the options to start sending transactions.
To do this, set the tracesSampleRate
option in your Sentry.init()
to a number between 0 and 1. With this option set, every transaction created will have that percentage chance of being sent to Sentry. (So, for example, if you set tracesSampleRate
to 0.5
, approximately 50% of your transactions will get recorded and sent.) That looks like this:
Sentry.init({
// ...
tracesSampleRate: 0.5,
});
To use the sampling function, set the tracesSampler
option in your Sentry.init()
to a function that will accept a samplingContext
object and return a sample rate between 0 and 1. For example:
Sentry.init({
// ...
tracesSampler: samplingContext => {
// Examine provided context data (including parent decision, if any) along
// with anything in the global namespace to compute the sample rate or
// sampling decision for this transaction
if ("...") {
// These are important - take a big sample
return 1;
} else if ("...") {
// These are less important or happen much more frequently - only take 1%
return 0.01;
} else if ("...") {
// These aren't something worth tracking - drop all transactions like this
return 0;
} else {
// Default sample rate
return 0.5;
}
};
});
For convenience, the function can also return a boolean. Returning true
is equivalent to returning 1
, and will guarantee the transaction will be sent to Sentry. Returning false
is equivalent to returning 0
and will guarantee the transaction will not be sent to Sentry.
The information contained in the samplingContext
object passed to the tracesSampler
when a transaction is created varies by platform and integration.
It includes at least the following:
// contents of `samplingContext`
{
// human-readable identifier, like "GET /users"
name: string;
// if this transaction has a parent, its sampling decision
parentSampled: boolean;
// The initial attributes passed to the span
attributes: Record<string, string | number | boolean>;
}
When using custom instrumentation to create a span, the tracesSampler
function will automatically receive the span name
and the initial span attributes
to use in its sampling decision.
Sentry.startSpan({
name: 'Search from navbar',
op: 'search',
attributes: {
testGroup: 'A3',
treatmentName: 'eager load',
},
});
// Will result in `tracesSampler` receiving:
function tracesSampler(samplingContext) {
/*
samplingContext = {
name: "Search from navbar",
attributes: {
testGroup: 'A3',
treatmentName: 'eager load',
},
}
*/
// Do not sample this specific span
return name !== 'Search from navbar';
}
Whatever a transaction's sampling decision, that decision will be passed to its child spans and from there to any transactions they subsequently cause in other services.
(See Distributed Tracing for more about how that propagation is done.)
If the transaction currently being created is one of those subsequent transactions (in other words, if it has a parent transaction), the upstream (parent) sampling decision will be included in the sampling context data. Your tracesSampler
can use this information to choose whether to inherit that decision. In most cases, inheritance is the right choice, to avoid breaking distributed traces. A broken trace will not include all your services.
tracesSampler: samplingContext => {
// always inherit
if (samplingContext.parentSampled !== undefined) {
return samplingContext.parentSampled
}
...
// rest of sampling logic here
}
If you're using a tracesSampleRate
rather than a tracesSampler
, the decision will always be inherited.
There are multiple ways for a transaction to end up with a sampling decision.
- Random sampling according to a static sample rate set in
tracesSampleRate
- Random sampling according to a sample function rate returned by
tracesSampler
- Absolute decision (100% chance or 0% chance) returned by
tracesSampler
- If the transaction has a parent, inheriting its parent's sampling decision
- Absolute decision passed to
startTransaction
When there's the potential for more than one of these to come into play, the following precedence rules apply:
- If a sampling decision is passed to
startTransaction
, that decision will be used, overriding everything else. - If
tracesSampler
is defined, its decision will be used. It can choose to keep or ignore any parent sampling decision, use the sampling context data to make its own decision, or choose a sample rate for the transaction. We advise against overriding the parent sampling decision because it will break distributed traces) - If
tracesSampler
is not defined, but there's a parent sampling decision, the parent sampling decision will be used. - If
tracesSampler
is not defined and there's no parent sampling decision,tracesSampleRate
will be used.
Our documentation is open source and available on GitHub. Your contributions are welcome, whether fixing a typo (drat!) or suggesting an update ("yeah, this would be better").